Memory state indicator check operations

ABSTRACT

Aspects include a computer-implemented method that includes receiving an instruction at a processor to perform an operation on a memory block having an address and accessing a state indicator by the processor without altering a value of the state indicator. The state indicator is stored in a memory location independent of the memory block, and accessing includes sending a request to an operator to return the value of the state indicator to the processor. The method also includes determining based on the value of the state indicator whether the memory block is in a pre-defined state.

DOMESTIC PRIORITY

This application claims the benefit of an earlier filing date from U.S. Non-Provisional application Ser. No. 14/755,732 filed Jun. 30, 2015, the entire disclosure of which is incorporated herein by reference.

BACKGROUND

The present invention relates generally to managing memory by a computer processor, and more specifically, to determining the state of blocks or regions of memory.

In modern computer systems, memory use is accomplished by a limited set of algorithms that manage the use of memory blocks or sections. Such functions include pre-fetch functions and memory allocation functions that manage memory to select blocks that are available for storage in response to input of data to memory and/or requests of data from various devices (e.g., CPUs, virtual machines, control units, external devices or users, etc.). Memory management operations include memory assignment operation, initialization operations, data movement operations (e.g., paging) and others.

SUMMARY

In one embodiment, a computer-implemented method includes receiving an instruction at a processor to perform an operation on a memory block having an address and accessing a state indicator by the processor without altering a value of the state indicator. The state indicator is stored in a memory location independent of the memory block, and accessing includes sending a request to an operator to return the value of the state indicator to the processor. The method also includes determining based on the value of the state indicator whether the memory block is in a pre-defined state.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as embodiments is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features, and advantages of the embodiments are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 depicts an embodiment of a computer system for processing and memory management;

FIG. 2 depicts an embodiment of a processor including memory management and memory state monitoring and/or indication capabilities;

FIG. 3 depicts an embodiment of a virtual memory address and addressing tables used by a processor to access memory locations;

FIG. 4 depicts an embodiment of a program-status word used by a processor to execute instructions;

FIG. 5 depicts an embodiment of an emulated computer system;

FIG. 6 is a flow diagram illustrating an embodiment of a method of processing data and managing memory by a processor; and

FIG. 7 is a flow diagram illustrating an embodiment of a method of determining whether a memory block is in a pre-defined state and/or performing an operation on a memory block.

DETAILED DESCRIPTION

Various embodiments of methods, systems and computer program products are provided for accessing and managing memory located in or accessible by a processor and/or computer system. Embodiments employ techniques that use knowledge or information regarding whether a memory block or area is in a pre-defined state. Program accessible state information is provided for blocks of memory that allow a processor to determine whether a block of memory is in some pre-defined state without inspecting all of the contents of the block of memory. A computer or processor (hardware or software), such as a processing unit, program or operating system, can use knowledge of whether a memory block is in a pre-defined state prior to accessing, operating on and/or inspecting the contents of the memory block. This knowledge can be used to avoid detailed inspection of the block and/or avoid redundant or unnecessary operations.

A state indicator may be incorporated in a data structure stored in a storage location accessible to the processor so that the processor can check the state indicator to determine whether a storage block is in a specific or pre-defined state. In one embodiment, the state indicator is configured to indicate a specific pre-defined state and allow a processor to identify the state without inspecting any of the contents of a memory block. An example of such a state indicator is a zero state or cleared state indicator. In another embodiment, the state indicator is configured to indicate a pre-defined state that may be one of a number of pre-defined states. A processor may inspect this pre-defined state indicator, and based on the pre-defined state indicator indicating that a memory block is in some pre-defined state, inspect only a portion of the memory block to identify the pattern of data values that are replicated across the entire memory block.

In one embodiment, a program, instruction or algorithm is provided that is executed by the processor to perform a method that includes checking or inspecting the value of the state indicator (e.g., a state indicator bit) without changing the value of the state indicator or otherwise disturbing the state indicator or contents of a data structure (e.g., a cache line or table array entry) in which the state indicator is stored. This embodiment enables examination of the state indicator without altering the state indicator, and enables the value associated with a block of memory to remain in a fixed, examinable state by a processor until a memory block associated with the state indicator is referenced by any operation that could subsequently lead to a modification within the memory block.

FIG. 1 illustrates an embodiment of a computer system 100, which may be used to implement methods and processes described herein, such as a personal computer, workstation, minicomputer, mainframe computer, server and/or network. The system 100 includes a processor 102 (e.g., a microprocessor and/or multi-core processor) and a main memory 104. The processor 102 is a hardware device for executing hardware instructions or software, including those stored in main memory 104, and may be a custom made or commercially available processor, a central processing unit (CPU), an auxiliary processor among several processors associated with the computer system 100, a semiconductor based microprocessor (in the form of a microchip or chip set), a macroprocessor, or other device for executing instructions. The processing unit 102 includes components such as a control unit 106, a processing unit 108 (e.g., an arithmetic logic unit) and a cache 110. Although the processor 102 is shown as a single processor 102, as described herein a processor may refer to multiple processors (e.g., a central processor complex (CPC)). Furthermore, the processor 102, the memory 104 and other components may be real or virtual, e.g., represented logically via a virtual machine.

Main memory 104 stores data and programs that are executed by the processor 102. Additional memory may be accessible to the processor 102 and other components of the system 100, such as internal and/or external secondary memory 116, such as a hard disk or database. As described herein, “memory” may refer to the main memory, any internal or external secondary and/or any other physical or virtual device or component that can store data and/or instructions. The memory (e.g., main memory 104 and secondary memory 116) may include one or combinations of volatile memory elements (e.g., random access memory, RAM, such as DRAM, SRAM, SDRAM, etc.) and nonvolatile memory elements (e.g., ROM, erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), programmable read only memory (PROM), tape, compact disc read only memory (CD-ROM), disk, diskette, cartridge, cassette or the like, etc.). Moreover, the memory may incorporate electronic, magnetic, optical, or other types of storage media. Note that the memory may have a distributed architecture, where various components are situated remote from one another but may be accessed by the processor 102.

Instructions in memory 104 may include one or more separate programs, each of which includes an ordered listing of executable instructions for implementing logical functions. In the example of FIG. 1, the instructions in the memory 104 include one or more operating systems 112 and programs 114. As used herein, “operating system” (OS) refers to any computer program, software, interface or device that is responsible for the management of computer resources and executing instructions. An OS, such as OS 112 in FIG. 1, essentially may control the execution of other computer programs and provides scheduling, input-output control, file and data management, memory management, and communication control and related services.

The cache 110 stores data from the main memory 104 and/or the secondary memory 116 used by the CPU to execute programs, receive data and send data. The cache 110 may include, but is not limited to, an instruction cache to speed up executable instruction fetch, a data cache to speed up data fetch and store, and a translation lookaside buffer (TLB) used to speed up virtual-to-physical address translation for both executable instructions and data. The cache 110 may be organized as a hierarchy of more cache levels (L1, L2, etc.). The cache 110 is divided into multiple cache lines 118 that contain, e.g., data fetched from main memory, tags indicting an address or location of the data in main memory, and flag bits. The cache lines may be stored and accessed as one or more cache arrays, e.g., a tag array and a data array.

Other components of the system 100 may include a memory controller 120 that may be incorporated in the processor 102 or as a separate circuit, other controllers such as a display controller, and interfaces to peripherals such as keyboards, a mouse and a display. An input/output (I/O) subsystem 122 facilitates transmission of data between the main memory 104 and/or secondary memory 116 and one or more I/O devices 124. The devices 124 may be internal to the computer system or external devices connected to the I/O subsystem 122 via any suitable connection, such as a network 126 (e.g., a local area network, fabric or the internet). The devices 124 may be any device or system that exchanges data with the main memory 104, such as clients, workstations, file servers, and peripherals such as printers, scanners, storage devices (e.g., external secondary storage 116) and output/display devices. Additional examples of devices 124 include card readers and punches, magnetic tape units, direct access storage devices, displays, keyboards, pointing devices, teleprocessing devices, communication controllers and sensor based equipment, to name a few.

In one embodiment, the I/O subsystem 122 is a channel subsystem, which uses one or more communication paths, such as channel paths 128 (or I/O channels) as the communication links in managing the flow of information to or from the devices 124. In one embodiment, the channel subsystem 122 includes one or more individual channels 130 that are each connected to one or more devices 124 via one or more channel paths 128. Each channel 130 includes processing electronics such as a local channel microprocessor and a local channel memory that is connected to and accessible by the local channel microprocessor. The local channel memory may include information such as a channel-program designation, a channel-path identifier, a device number, a device count, status indications, as well as information on path availability and functions pending or being performed. Also located within each channel 130 are one or more subchannels 132. Each subchannel 132 is a data structure located within a channel memory that provides information concerning an associated I/O device 124 and its attachment to the channel subsystem 122.

Modern computers typically manage memory as blocks or sections and utilize various schemes and techniques to manage access to various blocks and keep track of whether memory has been altered. For example, data may be stored in the main memory 104, secondary memory 116, caches 110 and other memory locations in fixed or variable size sections or blocks 134, which may take many forms. For example, memory may be divided into partitions (physical or logical), segments, pages and/or cache lines. Examples of memory blocks are described further below in conjunction with various embodiments and examples, but are not limited thereto. Memory blocks as described herein may be any type of memory partition or section used to divide a memory space, such as main memory, RAM, a cache, virtual memory and others, and is not limited to the specific embodiments described herein.

Memory management and general processing operations are used to perform a variety of tasks, such as initializing memory, reading and writing, assigning memory to users and devices, clearing memory (e.g., setting memory to zero) and others. Initializing memory generally includes setting memory blocks or regions to some predefined state (a set of data or values stored in the memory). One such state is a “cleared” state, in which a memory block or region has no user data or customer data (or any other data that can be stored in the memory block) stored therein. For example, a cleared memory block has all bits therein (e.g., in the block payload) set to zero, or to some other value indicating that no data is stored therein. Memory blocks can be set to various other states, which may include a repeating pattern of values, for purposes such as detecting memory faults and other errors. Memory may be cleared (set to a zero state in which the memory block is set to all zeros or otherwise has no user data, customer data or other data stored therein) or set to some pre-defined state in the course of memory management operations.

For example, when a processor sets up an amount of storage (referred to herein as a “memory space”), e.g., assigns memory pages or other types of memory blocks to a partition, the processor sets the memory space (or memory blocks making up the space) to an initial state. The initial state may be set by storing a pattern of values in the memory space, such as all zeroes (a zero state or cleared state), a repeating binary pattern or any other repeating pattern of data values(e.g., all ones or a repeating hexadecimal pattern).

In another example, a memory block may be part of memory in a server or disk that can be shared by multiple users. When memory is requested by a user, the processor typically selects a memory space including one or more blocks of memory and assigns that memory space to a user. When the user has finished using the assigned memory, it is returned to the system, and the memory space is cleared or set to some other state.

In yet another example, a processor (e.g., a CPU) stores copies of data from frequently used memory locations in a cache, which is typically divided into memory blocks referred to as cache lines. When the processor clears a cache, it sets all or some of the cache lines to zero, i.e., it sets all of the bits in each cleared line to zero.

If any of the blocks or other parts of the memory space were already set to zero in the above examples, clearing those blocks would represent an effective double clearing, which would result in an unnecessary use of processing time and resources. For example, memory being set to zero in a conventional system is often already set to zero. For example, a user may receive 100 MB of memory initialized or set to zero, but only store data in 80 MB of memory. The remaining memory was never touched and so is still zero. When this 100 MB of memory is released by the user, the entire 100 MB of memory is set to zero in the conventional system, even though 20 MB of the memory is already zero.

Many processing operations include copying or moving data from one memory to another. For example, if a processor sets up a new memory space or partition, data from memory blocks in other locations may be copied to the new memory space. In another example, a processor may need to page data into or from secondary storage locations such as hard disks. Typically, the processor just copies the appropriate memory blocks and all of the data therein to a new location. If a source memory block and a destination memory block have the same values stored therein (e.g., all zeros, one or a repeating hexadecimal value or word), copying between the source and destination would represent a redundant use of time and resources.

Embodiments described herein prevent such unnecessary use of resources by providing information to a processor that allows the processor to determine whether a block of memory is in a pre-defined state. For example, an indicator (referred to herein as a “pre-defined state indicator” or “state indicator”) or other information is provided that is accessible to a processor such that the processor can determine that one or more blocks are in a pre-defined state without having to inspect the contents of the blocks. The “contents” of a memory block, in one embodiment, are memory locations in the block at which customer data or other data can be stored (e.g., a memory block payload, as distinguished from metadata that may be stored with the memory block or elsewhere).

A “pre-defined state” refers to a state of a memory block in which data values are stored in a repeating pattern. For example, a memory block may store a repeated bit pattern (e.g., a binary pattern or a data word) in which a string of values of some length forms an identifiable pattern, and that pattern is repeated sequentially in the memory block. An individual pattern may be referred to herein as a “subset”. In one embodiment, under the assumption that the pattern is repeated across all lines within the memory block, a processor can identify the state of the memory block by inspecting only part of the memory block until the pattern is identified.

Techniques to determine if memory is already in a pre-defined state can include incorporating new data structures, existing data structures and/or additions to or extensions of existing data structures. For example, state indicators can be incorporated into existing change control bits, new metadata, or existing virtual to real mapping techniques or new data added to existing virtual to real mapping techniques for the purpose of determining if memory is in a pre-defined state.

A processing device or system, such as the system 100, includes information accessible by a processor (e.g., CPU, OS, controller, processing unit or module) to allow the processor to determine whether a block of memory has been set to a pre-defined state. This information represents knowledge that all or a portion of some memory is already set to the pre-defined state. Various methods are described herein that improve memory management performance by avoiding redundant operations, such as clearing operations, copying operations, re-initializations, overwrites and others, using the knowledge that some or all of the memory is already in the pre-defined state. Any existing technique for memory allocation or management may be used, with the addition of using this knowledge or information to determine whether a memory space or block is in a pre-defined state prior to inspecting the memory block or performing an operation on the memory block.

In one embodiment, each memory block includes or is associated with a program accessible state, indicator or other form of information that indicates whether the memory block is in a pre-defined state, i.e., at some state in which the memory block has a repeated pattern that is replicated over the memory block. In one embodiment, a pre-defined state indicator is stored with or otherwise associated with each individual memory block, and is independently managed relative to the memory block. The processor can determine whether the memory block is in a pre-defined state by inspecting the pre-defined state indicator. In one embodiment, in order to identify the particular state of the memory block, the processor inspects a subset or portion of the memory block (e.g., the first byte of a cache line) to identify the state. By utilizing the state indicator, the processor need only inspect the state indicator and/or an initial portion of the block to allow the processor to identify the state without inspecting the entire contents of the memory block, and use this information to improve processing by avoiding unnecessary operations, such as clearing a space that has already been cleared, or copying data between blocks that are in the same state.

In one embodiment, the pre-defined state indicator allows the processor to identify the pre-defined state without having to inspect any of the contents of an associated memory block. For example, the pre-defined state indicator is a clear indicator that indicates whether the memory block has been “cleared” or in a “cleared state”. A cleared block is a block that is in a state in which the memory block has no data stored therein and/or customer data or other data has been deleted (e.g., the block has been cleared to all zeroes or has not yet been used to store data). The processor may inspect or check the clear indicator and identify whether the associated memory block is in a cleared state without inspecting any of the contents of the memory block.

The pre-defined state indicator or information used by a processor or program may be embodied in any of various configurations. The pre-defined state indicator may be incorporated into any processor or program accessible data structure, including hardware and software structures. Examples of data structures include metadata, addressing tables (e.g., cache tables or arrays, page tables, index tables and dedicated state indicator tables or table entries), control register or data structure fields, encryption data, virtual machine or hypervisor data and others. A “data structure” that stores a pre-defined state indicator refers to any configuration of stored state indicator values and associated information that can be accessed by a processor and/or program independent of an associated memory block.

In one embodiment, the pre-defined state indicator may be included in metadata, control data structures and/or addressing data structures. For example, the pre-defined state indicator may be stored in the processor 102 as metadata received with instructions, fields in addressing tables, data structures in the channel subsystem 122, and/or metadata associated with memory blocks such as memory blocks 134 or cache lines 118. Non-limiting examples of the pre-defined state indicator and use of the pre-defined state indicator by a processor are discussed further below.

In another embodiment, the pre-defined state indicator may be stored in an array in memory of a multi-processor system, managed by a centralized facility, to ensure system cohesive management of the state indicators and to ensure proper system coherency management of the associated memory blocks. In this embodiment, the centralized facility marks a memory block as in a non-pre-defined state when a single segment of the memory block is modified or potentially modified by a processor or other associated device, in order to ensure an under-indication of the pre-defined state indicator and ensure proper system coherency and prevent possible data integrity issues. The processor marks the memory block as not being in a pre-defined state if the memory block is to be potentially modified, as indicating that a memory block exists in a predefined state when a segment is potentially modified can lead to improper handling of the memory block by a processor. Use of the state indicator thus ensures under-indication (thereby ensuring that at least the minimal number of operations occurs), and prevents and/or eliminates instances of over-indication of the state indicator that would result in improper action by a processor (e.g., potentially skipping a clear operation on a memory block).

In such embodiments, it remains desirable or necessary for a processor or processors to be able to inspect the state of associated memory blocks from time to time, as part of their normal processing operations, including the aforementioned memory clear and memory move operations. In such cases, the inspection of the state of the memory can cause the state indicator value to be reset, indicating that the memory block may not exist in a predefined state, and thus only allow the state indicator value to exist for one use. In order to overcome this shortfall, embodiments described herein provide a processor instruction and/or operation that can inspect the value of the state indicator and/or associated data, while allowing the state indicator value to remain unmodified. With said instruction and/or operation, it becomes possible to use the state indicator a multitude of times without altering the value of said state indicator, thus enabling a processor to perform multiple repeated operations on the memory block with optimal efficiency as previously described.

FIG. 2 shows an example of a processor 200 and components used by the processor 200 to perform processing and memory management functions. The processor may be configured as a CPU or other suitable type of processor, and performs functions including accessing and storing data and instructions in a memory (e.g., the main memory 104 and/or secondary memory 116) via a cache 202.

In this example, the processor 200 includes a translation unit 204 (e.g., a memory management unit) for transforming program addresses (e.g., virtual addresses) into real addresses of memory. The translation unit 204 includes a translation lookaside buffer (TLB) 206 for caching translations so that later access to an associated memory block does not require the delay of address translation. In one embodiment, data is fetched from memory by a control unit 208, which interacts with the cache 202 and includes storage and processing units such as a fetch unit 210 and a decode unit 212. The control unit 208 directs data to an execution unit 214. Multiple execution units may be included, such as an arithmetic execution unit, a floating point execution unit and a branch instruction execution unit. The control unit 208 may also be responsible for allocating memory to various users (e.g., external devices or virtual machines).

The translation unit 204 is used to translate between addresses used by the processor 200 and physical addresses. The TLB 206 is a hardware cache used by the translation unit 204 to store recently used entries of an address space table, e.g., a page table. For example, when a virtual address needs to be translated into a physical address, the TLB is searched first. If a match is found (a TLB hit), the physical address is returned and memory access can continue. However, if there is no match (called a TLB miss), the handler will typically look up the address mapping in the page table to see whether a mapping exists (a page walk). If one exists, it is written back to the TLB.

The processor 200 may include various storage components, including registers and caches that allow the processor 200 to perform various functions, such as instruction execution, configuration, storage and memory management functions.

The processor 200 communicates with a plurality of registers 216 during operation. An instruction operation code (opcode) determines which type of register is to be used in any particular machine instruction operation. For example, the processor 200 includes multiple general registers, status and control registers and memory block registers. General registers store information designated by instructions, and may be used as base address registers and index registers in address arithmetic and as accumulators in general arithmetic and logical operations.

Control registers provide for maintaining and manipulating control information, and are used to perform functions such as addressing and memory management functions. The bit positions in the registers are assigned to particular facilities in the system, such as program event recording, and are used either to specify that an operation can take place or to furnish special information required by the facility.

When the processor 200 wants to access and/or assign a memory block in main memory or a cache, the processor 200 and/or a processing unit therein (e.g., a memory management unit “MMU” or fetch unit) uses addresses stored in any suitable location, such as the cache 202, main memory or secondary memory. For example, the translation unit 204 accesses a list of addresses corresponding to blocks of memory or determines a virtual address and translates that virtual address into a corresponding real address. As discussed further below, the pre-defined state indicator may be stored as a flag or other field indication in an address, in an address table or in a dedicated list or table of state indicators that can be accessed without directly accessing the corresponding memory block.

In one embodiment, the processor 200 includes and/or communicates with a plurality of caches. For example, as shown in FIG. 2, the processor 200 is operatively connected to (e.g., via one or more busses) one or more level 1 (L1) caches 218, one or more level 2 (L2) caches 220, and at least one level 3 (L3) cache 222. The processor 200 may also be connected to one or more level 4 (L4) caches 224. One or more of the L1 cache 218, the L2 cache 220, the L3 cache 222 and the L4 cache 224 may include their own respective cache controllers for controlling various operations such as sending, receiving, and executing requests (also referred to as request signals). For example, cache controllers 226, 228, 230 and 232 are configured to control operation of the L1 cache 218, the L2 cache 220, the L3 cache 222 and the L4 cache 224 respectively.

The caches may be arranged or configured in a hierarchical structure to facilitate accessing memory and executing instructions. The caches are organized into levels based on how close the cache is to the processor and/or how quickly data in the cache can be accessed and processed. For example, the L1 cache is the lowest level cache, typically a relatively small and fast cache, the L2 cache is larger and slower than the L1 cache. The L1 and L2 caches may be mounted on the same module as the processor. The L3 cache is slower and larger than the L1 and L2 caches, and may be shared by multiple processors. The L4 cache is made from still larger and slower memory.

Addresses can be categorized in multiple ways. For example, addresses may be absolute, real, and virtual. The addresses are distinguished on the basis of the transformations that are applied to the address during a storage access. Address translation converts a virtual address to a real address. Prefixing converts a real address to an absolute address. In addition to the three basic address types, additional types are defined which are treated as one or another of the three basic types, depending on the instruction and the current mode.

An absolute address is the address assigned to a main storage location. An absolute address is used for a storage access without any transformations performed on it. All processing units and components in a configuration (e.g., the processor 102 and the channel subsystem 122 shown in FIG. 1) may refer to a shared main storage location by using the same absolute address. A real address identifies a location in real storage. When a real address is used for access to main storage, it is converted, by means of prefixing, to form an absolute address.

A virtual address identifies a location in virtual storage. When a virtual address is used for an access to main storage, it is translated by means of dynamic address translation, either to a real address which may be subject to prefixing to form an absolute address, or directly to an absolute address.

An example of a virtual address 300 is shown in FIG. 3. The virtual address 300 references a plurality of translation tables to obtain a real or absolute address. One or more of the translation tables may include a pre-defined state indicator so that a processor accessing a corresponding block of memory can determine whether the block is in a predefined state, such that if the block needs to be cleared or another operation is to be performed, the processor can avoid unnecessarily re-clearing, copying or other operations on the block.

The virtual address 300 includes fields or indexes to entries in translation tables in a hierarchy of translation tables. An exemplary virtual address 300 includes a region index (RX) 302, a segment index (SX) 304, a page index (PX) 306 and a byte index (BX) 308.

The virtual address 300 references entries in a region table, a page table and/or a byte table. A region table entry 310 includes a segment table origin field 312 that contains the address of a segment table entry 320, and additional fields such as a table offset (TF) field 314 indicating the offset (number of segments that are empty at the start of the segment table pointed to by the segment table origin field), a table type (TT) field 316 and a table length (TL) field 318 indicating the level and length of the table that contains the segment table entry.

The segment table entry 320 includes a page table origin field 322 that points to the table that this address uses, a page protection (P) bit 324 that indicates whether page protection applies to the segment associated with this entry, a common segment (C) bit 326 that controls use of the TLB, and a TT field 328. A page table entry 330 referenced by the segment table entry 320 includes a page frame real address 332 and a page protection (P) bit 334.

One or more of these tables, in one embodiment, includes a state indicator or other information that indicates whether the referenced page is in a pre-defined state. For example, as shown in FIG. 3, the page table entry includes a state indicator (S) bit 336. The S bit 336 may be set to a value (e.g., one) when the page is initially set up or when the page is set to a pre-defined state, and set to another value (e.g., zero) when data is stored to the page. Each time the page is set to a pre-defined state (e.g., initialized or cleared), the S bit is set accordingly (e.g., to one) so that when a processor subsequently accesses the page, it can determine whether the page is in a pre-defined state before determining whether to access or perform an operation on the page.

In one embodiment, the S bit may be an indicator that indicates to the processor that a memory block is in a state that can be identified by the processor without any inspection of the contents or data stored in the memory block. For example, the S bit is a clear indicator bit that indicates that the memory block is in a cleared state, i.e., is all zeros or otherwise has no data stored therein.

In another embodiment, the S bit is an indicator that indicates more generally that the memory block is in some pre-defined state. For example, the pre-defined state is a repeating pattern of data values replicated across the entirety of the memory block. The processor inspects the S bit, and if the S bit is active or “on”, inspects a portion or subset of the stored data or contents until a pattern is identified, and identifies the state based on the pattern.

As discussed above, a CPU or other processor uses the address 300 and stored information such as the tables 310, 320 and/or 330 to translate the address to a real address of an accessed or requested memory block. The processor may treat the address as a real address or a virtual address.

In use, if the processor inspects the S bit 336 and the value of the bit indicates that a corresponding page is in a pre-defined state, the processor inspects a first portion of the page until a pattern is identified. For example, the processor inspects a first portion (e.g., the first 8 bits or 4 bytes) and identifies a pattern, such as all zeroes, all ones or a hexadecimal pattern. Based on this pattern, the processor can determine the current state of the page.

FIG. 3 shows an example of a data structure that can be used in conjunction with the S bit 336. In this example, the processor follows instructions (e.g., opcode) to check a state table 338, which associates pre-defined states with bit patterns or other data patterns. The state table may be accessed based on program instructions, a pointer 340 or other information.

Another embodiment that incorporates a pre-defined state indicator is discussed in conjunction with FIG. 4, which shows an example of control information stored by a CPU or other processor to control execution of instructions and memory allocation functions. Control information may be loaded to the processor to a storage location such as a control register.

FIG. 4 shows an example of control information configured as a program status word (PSW) 400. The PSW is an area of memory or a hardware register which contains information about the program state used by an operating system and the underlying hardware. The PSW includes an instruction address, condition code, and other fields. In general, the PSW is used to control instruction sequencing and to hold and indicate the status of the system in relation to the program currently being executed. The active or controlling PSW is called the current PSW. By storing the current PSW during an interruption, the status of the CPU can be preserved for subsequent inspection. By loading a new PSW or part of a PSW, the state of the CPU can be initialized or changed.

The PSW 400 shown in FIG. 4 includes various fields and bits. A DAT Mode (T) bit 402 controls whether dynamic address translation (DAT) is used. When the bit 402 is zero, DAT is off and logical and instruction addresses are treated as real addresses. When the bit is one, DAT is on, and the dynamic address translation mechanism is invoked.

Other fields include an Address Space Control (AS) field 404 that is used in conjunction with the T bit 402 to control the translation mode. A Condition Code (CC) field 406 is set to a value of 0, 1, 2, or 3, depending on the result obtained in executing certain instructions. An Instruction Address field 408 designates the location of the leftmost byte of the next instruction to be executed.

A key (Key) field 410 forms an access key for storage references by the CPU. If the reference is subject to key controlled protection, a PSW key in the Key field 410 is matched with a storage key when information is stored or when information is fetched from a location that is protected against fetching. The Key field 410 is used to protect the main storage or other storage to control access to various memory blocks by users or tasks. The Key field 410 includes an access control field 412 including a storage key that is compared to access control bits in the memory block being referenced to determine whether the task accessing the memory block is allowed to access that storage. A Fetch protection (F) bit 414 indicates whether protection applies to fetch and/or store operations, a reference (R) bit 416 is associated with DAT, and a Change (C) bit 418 is set to one when information is stored in the corresponding memory block.

In one embodiment, a pre-defined state indicator is incorporated into the PSW to indicate whether a storage reference in the instruction refers to a memory block that has been set to or is in a pre-defined state. In this example, the pre-defined state indicator is located as a bit referred to as a State Indicator (S) bit 420 in the Key field, although the CI bit may be incorporated in other locations, fields or bit positions in the PSW. The state indicator 420 may prompt the processor to access a data structure that associates an initial data pattern or bit pattern in a memory block to a pre-defined state.

It is noted that the fields and bit locations discussed herein are exemplary and non-limiting. The S bit, pre-defined state indicator or other state information may be included in any suitable location or field in the address, tables, table entries and PSW discussed above. In addition, the state information may be stored in other locations and/or data structures used by a processor to manage and/or access memory.

In addition to the configurations described above, embodiments described herein may be incorporated into emulated computers and computer systems. Computer environments, including processors, memory, control units, interfaces, I/O subsystems and other components, may be virtualized. In addition, a computer or environment may be virtualized into multiple separate systems using, e.g., virtual machines.

FIG. 5 shows an example of an emulated (virtual) host computer system 500 that includes memory state information. The system 500 emulates a host computer system 502 and includes an emulated host processor 504 that is realized through an emulation processor 506. Physical memory 508 is partitioned into host computer memory regions 510, also referred to in some instances as logical partitions (LPARs). Each region stores a hypervisor 512 and one or more virtual machines (VMs) 514, each of which runs a guest operating system 516 and various applications 518.

In one embodiment, each virtual machine has access to memory state information such as a pre-defined state indicator for each virtual memory block accessible by the virtual machine 514. For example, each VM 514 (or group of VMs) has access to a pre-defined state indicator table 520 that can be inspected by a VM prior to fully inspecting or performing an operation on a corresponding memory block or otherwise accessing or inspecting the memory block. The state indicator table 520 includes a state indicator field associated with each memory block address accessible by a VM that can be set to indicate whether a memory block is in a pre-defined state. The state indicator table 520 or another suitable data structure may provide information that allows a VM or processor to determine the state of the memory block based on a pattern of a subset of the data stored therein.

FIG. 6 illustrates aspects of an embodiment of a method of processing data and managing memory by a processor. The method 600 may be performed by any suitable processor or computer system capable of accessing memory blocks or other memory locations. Exemplary processors include one or more components of the computer system 100, the processor 200 and/or the emulated computer system 500. In one embodiment, the method includes the steps represented by blocks 601-604 in the order described. However, in some embodiments, not all of the steps are performed and/or the steps are performed in a different order than that described.

At block 601, the processor sets up memory spaces and memory blocks, and assigns memory spaces and blocks to virtual and/or physical devices. A memory block may be any region or area of storage, such as a memory page or other block in main memory or secondary memory, a cache or a cache line.

For example, the processor initializes each memory block to an initial pre-defined state in which the memory block is set to a series of data values that follow a repeating pattern. For example, each memory block is set to a repeating pattern such as all zeroes (a zero state), all ones, 0xFFFFFFFF, 0xDEADBEEF, 0xABCDEF01, 0xBAD1BAD1, or other patterns.

As part of the set up process, the processor may check or inspect a pre-defined state indicator stored in a suitable location, such as a configuration array, metadata stored with individual memory blocks or spaces, and/or addressing tables. Based on the pre-defined state indicator, the processor determines whether each block or group of blocks is in a cleared or other pre-defined state. An exemplary pre-defined state indicator is the S bit 420.

If the pre-defined state indicator is active, the processor assumes that the block has a repeating pattern of data. The processor then examines a portion of the block, e.g., a first line of a page or a subset of the page such as the first 8 bits. The processor then identifies the state of the block, and can use this knowledge to improve processing operations.

The processor can use the pre-defined state indicator to determine whether a memory block is in an initialized state to avoid re-initializing the memory block if possible. If a memory block or space is already in an initialized state, the processor assigns the block or blocks to a partition or VM without first initializing the memory block or space. If the memory block or space is not in an initialized state, the processor initializes the memory block, and then sets the pre-defined state indicator to indicate that the memory block or space is now in an initialized state.

In another example, a VM has a number of partitions running thereon. The VM sets up a new partition using a base image containing a memory space (e.g., scratch space) to expedite setup. In setting up a new partition, the VM the VM inspects a pre-defined state indicator or other state information (e.g., the state indicator table 520) to determine whether a portion of the base image represents memory that is cleared or in a pre-defined state. If a portion of the memory is in a pre-defined state, the VM need only copy data to the new partition from portions of the memory that, thus avoiding copying redundant portions and avoiding unnecessary data movement operations for the portions.

In some instances, a processor receives an instruction to clear or set a memory block to some set of values (such as a page clear/pad to zero or, e.g., all values of 0xFF) during an exception check on the page (which normally requires fetching a page line and key from memory). The processor can check the pre-defined state indicator (e.g., the S bit). Upon observing that the indicator is active, the processor can compare the pad pattern of the page to determine whether the page is already set entirely to the instructed set of values (e.g., 0xFF). If the pad pattern matches this value, the clear/pad can be completed without issuing any stores to memory.

At block 602, the processor receives a request from a device for access to a memory space or an instruction to perform an operation on the memory space. In response, the processor selects an available memory space or group of memory blocks, and determines based on the pre-defined state indicator whether the available space or group of blocks is in a pre-defined state.

At block 603, if a memory block is associated with a pre-defined state indicator that indicates that the memory block is in a pre-defined state, the processor inspects a subset of the memory block. The pattern of data values in the subset of the memory block is compared to known or stored data value patterns. If a match is found, the processor identifies the actual state of the memory block.

At block 604, the processor utilizes pre-defined state indicators to facilitate executing instructions and performing operations that involve memory blocks with identified pre-defined states.

An example of an operation includes migrating data between a main memory and secondary memory (e.g., disks). If a memory space including multiple memory blocks (e.g., pages) needs to be transferred from disk, the processor (e.g., via an I/O controller or subsystem) checks pre-defined state indicators to determine whether any portion of the memory space is in a pre-defined state.

The processor may check pre-defined state indicators associated with pages or other memory blocks that are to be transferred to or from secondary memory. By the checking the indicators and inspecting a first portion of each block, the processor can determine what if any pre-defined state each block is in. If the current state of a page or other memory block is the same as would be the final state of the memory block after transferring, the processor can complete the operation for that block immediately without having to copy data to or from the block.

In one embodiment, processors and systems described herein include functionality to allow a processor to inspect a pre-defined state indicator without changing the value of the state indicator or disturbing the state indicator. This functionality allows the pre-defined state indicator to be checked during each operation while preserving the integrity of the state indicator and allowing the processor or other operators to check the state indicator during subsequent operations.

For example, a processor sets the pre-defined state indicator to a first value (e.g., one or a value indicating “on”) when an associated memory block is configured (e.g., during initialization) to a cleared state or other pre-defined state. The pre-defined state indicator is stored in a data structure such as a page table entry. When the memory block is referenced, i.e., accessed by the processor as part of an operation that could potentially change the state of the memory block, the pre-defined state indicator is reset to a second value (e.g., zero of a value indicating “off”).

The processor in this example resets (turns off) the pre-defined state indicator whenever the memory block is referenced, because once the memory block is referenced, the memory block could be changed. Because the memory block may have been changed when it was pulled outside of its scope (e.g., resident only in main memory or secondary memory), leaving the pre-defined state indicator in the “on” state may result in the state indicator wrongly indicating that the memory block is in a pre-defined state. Any subsequent operations looking to optimize based on the state indicator may perform the wrong type of operations if the state is not accurately reported or under-indicated.

Because of this, in this example, whenever a processor checks the pre-defined state indicator in preparation for executing an operation and determines that the memory block is in a pre-defined state, the processor resets the indicator, thus allowing only one check on the state to occur before it is turned off or reset. If repeated operations occur, even if such operations do not change the state of the memory block, the memory block contents may need to be inspected before setting the state indicator after an operation that did not change the state of the memory block. This repeated inspection of memory block contents could result in the system failing to achieve a desired optimization.

For example, a store pad operation, which clears memory by overlaying it with a replicated pattern of data, targeting the same page in a system multiple times in a row would only be able to eliminate redundant operations on the even numbered repeats, as the first pad operation would set the state indicator bit, the second pad operation would skip the clearing but dirty the state bit, the third pad operation would occur and set the state bit, and so on.

In order to prevent such situations, a processor may be configured to access, inspect and/or return a data structure associated with a memory block under inspection without changing the value of the state indicator and/or without causing a situation in which the state indicator could become “dirty”, i.e., potentially indication the wrong state.

An operator (e.g., a software or hardware component running a subroutine or other set of instructions) is configured to perform a method that includes inspecting a state indicator associated with a memory block located at an address or set of associated addresses (cache line or memory) and determining the value of the state indicator without changing the value of the state indicator. The operator may be the processor that is to perform an operation on the memory block (e.g., initialization or paging operation) or a separate operator such as a cache controller or software program.

In one embodiment, the method includes receiving an instruction for a processor to perform an operation on a block of memory or a memory space having multiple blocks of memory. For each memory block, the processor checks a state indicator that is stored in a data structure independent of the memory block. The processor may request another operator to inspect the state indicator and return a value of the state indicator to the processor.

For example, the processor, upon receiving an instruction associated with a memory block, inspects an associated state indicator stored in a cache or other memory location. If the state indicator indicates that the memory block is in a pre-defined state, the processor identifies the state, and determines whether the operation will potentially change the state of the memory block. If the operation is anticipated to not change the state (e.g., the instruction is to initialize the memory block and the memory block is already in an initialized state), the processor completes the operation without modifying the memory block or changing the value of the state indicator. In this way, the integrity of the state indicator is preserved, and the next time that the memory block is accessed, the entity accessing the memory block can inspect the state indicator.

If the state indicator indicates that the memory block is not in a pre-defined state, or the memory block is in a pre-defined state and the operation will change that state, the processor can inspect and access the state indicator (and data structure storing the state indicator) as needed to set the value of the state indicator at the end of the operation.

In one embodiment, the state indicator is stored in a memory location that is different than the memory location (e.g., cache) used by the processor to inspect and/or change the state indicator. If the processor determines that the operation will change the state of the memory block, the processor moves a portion of the data structure (e.g., a page table entry or state indicator table entry) into an appropriate cache, and sets or resets the state indicator based on the state of the memory block after the operation.

FIG. 7 illustrates aspects of an embodiment of a method of determining whether a memory block is in a pre-defined state and/or performing an operation on a memory block. The method 700 may be performed by any suitable processor or computer system capable of accessing memory blocks or other memory locations. Exemplary processors include one or more components of the computer system 100, the processor 200 and/or the emulated computer system 500. In one embodiment, the method includes the steps represented by blocks 701-704 in the order described. However, in some embodiments, not all of the steps are performed and/or the steps are performed in a different order than that described.

The method 700 is described in conjunction with the processor 200 and hierarchical caches described above, but is not so limited. The method 700 may be performed solely by a processor, by a processor in conjunction with another operator, and may be performed using any number or configuration of caches or other memory locations used to store state indicators and/or execute operations.

At block 701, a processor such as the processor 200 receives an instruction to perform an operation on a memory block or group of memory blocks. An example of an operation is an initialization operation or a clear operation (e.g., a store pad); however the method 700 can be used in conjunction with any operation that involves accessing or processing one or more memory blocks. For example, the processor 200 receives an instruction to initialize or clear a memory block.

At block 702, the processor checks a pre-defined state indicator associated with the block by performing a test or checking the state indicator at a location that is different than the memory location used by the processor to execute the operation. The processor checks the state indicator without caching, moving or otherwise disturbing the state indicator value. In one embodiment, the processor issues a request to an operator to determine whether the memory block is in a cleared state or in some pre-defined state.

For example, a page table array and/or other data structure is stored in the L2 cache 220 (or the L3 and/or L4 cache), and the processor 200 requests that the L2 cache controller 228 return a value of a state indicator (e.g., the S bit) associated with a memory block. The processor 200 receives this value and determines whether the memory block is in a cleared state or other pre-defined state.

At block 703, if the value of the state indicator indicates that the memory block is in a cleared state, the processor 200 completes the operation on the memory block without directly inspecting the page table array or other data structure stored in the L2 cache 220. The processor may complete the operation without caching or accessing the memory block (e.g., for an initialization operation), or may cache the memory block and complete the operation without accessing or modifying the state indicator or the data structure. The state indicator remains at its current value and can be reliably checked by the processor or other operator for a subsequent operation.

At block 704, in one embodiment, if the value of the state indicator indicates that the memory block is in a pre-defined state, the processor 200 inspects a subset of the memory block at its stored location (e.g., the L3 cache 222, the L4 cache 224, main memory or other location) without caching any of the memory block in the L1 cache 218. The pattern identified in the subset is compared to test patterns or other information, and the state of the memory block is identified.

In one embodiment, the processor 200 requests that another operator inspect the subset and identify at least the pattern, or the processor otherwise inspects the subset without caching the memory block or any portion thereof. For example, the processor 200 requests that the L3 cache controller 230 inspect a subset of the memory block, and return the pattern and/or compare the subset pattern to the test patterns and return an identification of the state of the memory block.

Upon identifying the state of the memory block, the processor 200 determines whether the memory block needs to be cached or otherwise accessed to perform the operation. If the identified state is the same as the state to which the memory block is to be initialized, the processor 200 completes the operation without accessing or modifying the memory block. The processor 200 also completes the operation without accessing or modifying the state indicator or the data structure. The state indicator remains at its current value and can be reliably checked by the processor or other operator for a subsequent operation.

At block 705, if the memory block is not in a pre-defined state or the memory block has been changed due to an operation, the processor 200 copies the memory block (or portion thereof) to the L1 cache 218 and clears the memory block or initializes the memory block to some initial pre-defined state. In addition, the processor 200 copies the state indicator (e.g., a page table entry) to the L1 cache 218 or other cache, sets the state indicator to indicate whether the memory block is cleared or set to a pre-defined state, and returns the updated state indicator to the L2 cache 220.

It is noted that the systems and methods utilizing knowledge of whether memory is in a pre-defined state are not limited to the specific embodiments described herein. The systems and methods may incorporate any technique to improve the performance of operations such as copying memory from one location to another, or avoiding unnecessary operations, where the technique uses knowledge that some or all of the memory being moved is already in a pre-defined state.

An example of an operation that can be improved using embodiments described herein is an I/O operation in which data is moved from main memory or internal storage to a secondary storage or external device. An operating system can maintain a list of pointers to common pre-initialized page states, and can assign physical memory to a partition based on their preferred pre-initialized state. In the case of paging memory out to disk, the operating system can use the state indicator to mark pages as reclaimed, both for zero state pages and for any permutation that is common to the workloads running on a system.

Another example of an operation utilizing the pre-defined state information described herein includes encryption and compression techniques, whereby the pre-defined state indicator can be used to determine whether a memory space (or portion thereof) being encrypted or compressed is already encrypted or compressed. By making such a determination, a system processor can avoid subsequent fetch operations to the remainder of the memory block(s), continuing the encryption or compression operation on the existing cached portion of the memory block, given that the subsequent blocks have been determined to exist in the same state.

Technical effects and benefits of some embodiments include improvements in processor or computer functionality by, e.g., reducing the time and resources required to access or allocate a block of memory. For example, embodiments described herein produce benefits relative to prior art systems, such as reduced event latency, reduced system resource utilization, reduced system queuing and reduced system power use, as redundant operations can be avoided and movement cases could be optimized to reduce their visible effects. In addition, embodiments improve the functioning of processors and/or programs that utilize state indicators, by ensuring the integrity of state indicators and subsequent system optimizations without requiring redundant or unnecessary operations on associated memory blocks or memory regions.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

The present invention may be a system, a method, and/or a computer program product. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present invention.

The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of the computer readable storage medium includes the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as punch-cards or raised structures in a groove having instructions recorded thereon, and any suitable combination of the foregoing. A computer readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire.

Computer readable program instructions described herein can be downloaded to respective computing/processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and/or a wireless network. The network may comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and/or edge servers. A network adapter card or network interface in each computing/processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing/processing device.

Computer readable program instructions for carrying out operations of the present invention may be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like, and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The computer readable program instructions may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer readable program instructions.

These computer readable program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer readable program instructions may also be stored in a computer readable storage medium that can direct a computer, a programmable data processing apparatus, and/or other devices to function in a particular manner, such that the computer readable storage medium having instructions stored therein comprises an article of manufacture including instructions which implement aspects of the function/act specified in the flowchart and/or block diagram block or blocks.

The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process, such that the instructions which execute on the computer, other programmable apparatus, or other device implement the functions/acts specified in the flowchart and/or block diagram block or blocks.

The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.

The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein. 

What is claimed is:
 1. A computer-implemented method, comprising: receiving an instruction at a processor to perform an operation on a memory block having an address; accessing a state indicator by the processor without altering a value of the state indicator, the state indicator stored in a memory location independent of the memory block, wherein accessing includes sending a request to an operator to return the value of the state indicator to the processor; and determining based on the value of the state indicator whether the memory block is in a pre-defined state.
 2. The method of claim 1, wherein determining is performed without changing the value of the state indicator.
 3. The method of claim 1, further comprising: based on the value of the state indicator indicating that the memory block is in the pre-defined state, sending a request to return a subset of the memory block to the processor; and identifying the pre-defined state of the memory block based on the subset of the memory block.
 4. The method of claim 1, further comprising: based on the value of the state indicator indicating that the memory block is in the pre-defined state, identifying the pre-defined state based on the value of the state indicator without at least one of directly inspecting any contents of the memory block and returning any of the contents to the processor.
 5. The method of claim 1, further comprising: based on the state indicator indicating that the memory block is in the pre-defined state, and based on determining that the operation will not result in a change of state of the memory block, performing the operation without changing the value of the state indicator.
 6. The method of claim 1, further comprising: based on the state indicator indicating that the memory block is in the pre-defined state, and based on determining that the operation will potentially result in the change of state, changing the value of the state indicator.
 7. The method of claim 1, wherein the processor is coupled to a plurality of hierarchical caches including at least a first cache configured to be used by the processor for executing the operation, and a second cache configured to store a data structure including the state indicator.
 8. The method of claim 7, wherein accessing the state indicator includes sending the request to a cache controller to inspect the data structure at the second cache and return the value of the state indicator without the processor moving the state indicator to the first cache. 